Exercise Physiology Flashcards
Energy systems -
Response of energy systems to physical activity
- Anaerobic - adenosine triphosphate-creatine phosphate (ATP-CP)
- lactic acid
- Aerobic
Rate of ATP production =
How quickly ATP is resynthesised
Yield =
How much ATP is resynthesised
ATP
A chemical compound called adenosine triphosphate (ATP) is responsible for producing energy for movement
When ATP is broken down energy is released
ATP —> ADP + Pi (inorganic)
Fuels required for resynthesis of ATP
- energy is released during the breakdown of ATP in to Adenosine diphoshate (ADP) and third phosphate - represents the immediate source of energy that can be used by muscle cells to perform
- when the body is performing physical work it is converting chemical energy (ATP) produced by chemical reactions into mechanical energy (muscular contractions)
What is ATP
- only a very small amount of ATP is stored within muscles, so ATP must continually be rebuilt / resynthesised so that the energy can be provided for longer periods of time
- ATP can be rebuilt / resynthesised from the breakdown of phosphate creatine (PC) or from the breakdown of macronutrients (carbohydrates, proteins and fats) from of diet
ATP-CP energy system
An immediate energy system that does not require oxygen
Fuel: uses a combination of stored ATP + the stored creatine phosphate
Intensity: maximum efforts >95% max HR
Duration: short duration (fuel depleted after 10 secs)
Rate of resynthesis: very fast
Yield: low
ATP-CP advantages and disadvantages
Advantages:
- high intensity exercises
- rate of resysnthesis
- stored in muscles
Disadvantages:
- low yield
- duration
Anaerobic glycolysis system (lactic acid)
Relies on breakdown of glycogen, in the absence of oxygen, to produce energy
Fuel: carbohydrates
Intensity: 80-95% max HR
Duration: will take over as predominant system when ATP-CP system fatigues (PC stores depleted at around 5 - 10 secs) predominant 10-6- second events. Peak power is usually reached between 5-15 secs)
Rate of resynthesis: fast
Yield: low - medium - 2ATP
Anaerobic glycolysis system advantages and disadvantages
Advantages:
- intensity
- rate
Disadvantages:
- lactic acid - cramps
- low yield
- slow recovery (if lactic acid present)
Glycolysis
Takes place in the cytoplasm, where the enzymes required are present
Glycolysis is to destroy or break down glucose
Because oxygen is not present, the glycogen is not totally broken down and a by-product called lactic acid (lactate + hydrogen ions) is formed
Lactic acid
Use of the anaerobic glycolysis system results in the production of lactic acid.
What happens when we accumulate lactic acid?
- Lactate purely serves as an indicator that the body is no longer working aerobically. It also represents the accusation of Hydrogen+ ions
- Although 80% of lactate diffuses from the muscles & transported back to the liver for conversion to glucose or glycogen some hydrogen ions (H+) accumulate in muscle tissue
- An increase in lactate levels means pH levels are dropping (a pH level of 7 indicates neutral - less than 7 means your muscles are becoming acidic) which decreases the activity of enzymes which break down glycogen
- Contracting muscles don’t like acid, so when pH levels drop, the stop working as a feedback mechanism to prevent injury. As a result, the anaerobic glycolysis pathway is compromised and exercise intensity must be reduced
Aerobic system (fuel, …
Fuel: carbohydrates, fat and protein (depending on intensity, duration)
Intensity: during rest and at sub-maximal intensities <80% HR max
Duration: gradual increase in contribution as O2 becomes available. Predominant energy after 30-60sec ((2 min <) depending on intensity)
Rate of Resynthesis: slow
Yield: very high (36 -38 ATP)
Aerobic system advantages and disadvantages
Advantages:
- high yield
- longer duration
- no by products that effects fatigue
Disadvantages:
- low intensity
- slow rate of resynthesis
Aerobic glycolysis
The breakdown of glycogen in the presence of oxygen to produce energy, carbon dioxide, water and heat
Once O2 becomes available to the muscle cell a different chemical reaction known as aerobic glycolysis takes place
The aerobic system takes a while to get going because a number of processes need to occur:
- lungs work harder to bring in more O2
- heart pumps harder to transport O2 rich blood to the muscles
- arteries expand to increase blood flow
Aerobic system (2)
This system has the greatest capacity to produce ATP but is the slowest to do so (high yield but low rate)
The fuel source used by the aerobic system (carbohydrates and fats) depends on the intensity and ration of the activity
- Carbohydrates for the first 90 minutes then fats up till 4 hours
- CHO are the preferred energy source during high intensity exercise as fats can produce more ATP than CHO but they require more oxygen to produce an equivalent amount of ATP
Steady state exercise
- Oxygen consumption rises sharply during first minutes of exercise
- This consumption begins to plateau between 3-4 minutes and will remain stable for the duration of exercise
- This means there is a balance between energy required by working muscles and ATP produced by the aerobic pathway
- This is referred to as Steady State “exercise”
Oxygen deficit
- When excessive commences, O2 consumption does not reach “steady state” plateau immediately
- Oxygen deficit is the state in which there is a discrepancy (shortfall- (lack)) between oxygen supply and demand and the oxygen required to meet the energy requirements of the activity
- Energy used during O2 deficit period is supplied through anaerobic pathways
- Endurance-trained athletes reach steady state more rapidly, with smaller oxygen deficit
The oxygen deficit occurs because the respiratory and circulatory systems take some time to adjust to the new oxygen demand and, consequently, the amount supplied lags behind the amount needed
Oxygen deficit = oxygen consumption, O2 usage
- what your breathing in compared to what your body’s
The bodies systems will adjustments to increase oxygen supply.
- increased respiratory frequency. - breathes
- increased tidal volume. - air per breathe
- increased heart rate
- increased stroke volume. - blood per beat
EPOC stands for
Excess post-exercise oxygen consumption
(Oxygen debt)
EPOC
EPOC is the amount of oxygen consumed during the recovery period (after the end of the activity).
It’s an increased rate of oxygen consumption above that is required during rest
Oxygen can be viewed as the ‘currency’ the body uses in order to ‘purchase’ (resynthesise) ATP.
In other words, oxygen must be used in order for ATP to be produced.
After the cessation of exercise, oxygen uptake or consumption does not immediately return to resting levels, despite the fact that the demand from ATP resynthsis decreases dramatically. Rather, oxygen consumption remains temporarily elevated. This elevated oxygen consumption, which exceed that normally experienced at rest, is referred to as excess post-exercise oxygen consumption (EPOC)
The purpose of EPOC is to:
- replenish ATP-CP stores
- removes lactic acid
- replacing depleted oxygen stores in body
- supply oxygen to heart and respiratory muscles-still active
- supply oxygen to body tissues to be used because of increased body temperature resulting from exercise
Food fuels v chemical fuels
Energy from the breakdown of PC or the stored forms of CHO, fats and protein are used to re-join ADP & inorganic phosphate (Pi) to resynthesise ATP
Carbohydrates
- broken down into glucose for blood transportation
- stored as glycogen in the muscles & liver
- carbohydrates (sugars & starches, in foods such as fruit, cereal, bread, pasta & vegetables) are the body’s preferred source of fuel, particularly during exercise
Glycemic Index (GI)
Ranking of carbohydrates based on their immediate effect on blood glucose (blood sugar) levels.
Measured on a scale of -100
Low GI foods - food
- apples
- lentils
- kidney beans
- peanuts
- navy beans
- sausages
Moderate GI foods - food
- corn
- peas
- white pasta
- sweet potatoes
- oranges
- oatmeal
High GI foods - food
- pure glucose which has a GI of 100
- honey
- white bread
- white rice
- gel shot
- hot chips
High GI foods
- break down quickly during digestion - therefore have immediate effect on increasing blood sugar levels
- best consumed during and immediately after the event
High GI foods - during exercise
Rapid absorption and release of energy into bloodstream provides opportunity to top up glycogen stores, helping to delay the depletion of glycogen stores
High GI foods - immediately after exercise ( within 30 mins)
Immediately after exercise muscles are most responsive to topping up their fuel supplies, therefore it’s GI foods need to be consumed within 30 minutes of the activity finishing
Low GI foods
- break down slowly during digestion resulting in a slow release of glucose into the blood stream
- best consumed as part of the pre-event meal and after the event to replenish supplies
Low GI foods - Pre-event meal (1-4hrs prior)
Slower release of glycogen into bloodstream helps keeps blood glucose levels topping up prior to race
Low GI foods - After exercise (1-24hrs post exercise)
Assists with repletion of muscles and liver glycogen stores in the 24hr post exercise
Rebound hypoglycaemia
- athletes must be careful they don’t consume high GI foods 30-120min prior to event as it may cause rebound hypoglycaemia
- immediately after eating CHO, there is a rise in blood sugar levels resulting in the hormone insulin being released into the blood and lowering blood sugar levels
- when an athlete consumes high GI foods just prior to physical activity, we see a rapid rise in blood sugar levels causing an overshoot in insulin release
- this insignificant reduces blood sugar levels which impairs CNS functioning during exercise causing a negative effect on performance
Carbohydrate loading
Nutritional intervention aimed at delaying the depletion of glycogen stores. It occurs when the athlete increases the amount of CHO consumed prior to competition with the aim being to store extra glycogen in the liver and muscles. There are two main methods to load
During exercise, CHO stores become depleted, causing an increase in the use of fats for energy
Fats have a high oxygen cost than CHO, therefore the body must reduce exercise intensity
1 day method - carb loading
- consume approximately 8-10g/kg body weight of carbohydrates the day before competition (approx 700g stored in muscle and liver)
This is equivalent to eating almost 3 loaves of bread in 1 day - you need to use supplements!! - tapering or reducing training load is required to spare muscle glycogen stores
3 day method - carb loading
- consume approximately 7-8g/kg body weight of carbohydrates for 3 days leading up to competition (approx 700g stored in the muscle and liver)
- players can still exercise, however there is significant tapering occurring leading up to competition so as to not deplete glycogen stores
- 3 day method is not suitable for sports which require athletes to perform every week - a 3 day temper leading up to match on Saturday would require a taper starting on Wednesday which is not ideal
Carb loading advantages
- CHO loading avoids the depletion of glycogen stores by increasing muscle and liver glycogen levels
- By sparing glycogen, it allows the aerobic athletes to maintain a higher intensity for a longer period of time
Carb loading disadvantages
- binding of H2O to CHO molecules increases water absorption, causing an increase in weight
Glycogen sparing
Is the ability of an athlete to spare glycogen supplied by using an alternative fuel source during physical activity
Glycogen sparing - 4 ways
Training effects
Caffeine consumption
Pre - event meal
During the event meal
Relative contribution of fuel (CHO and fats) at varying exercise intensities - crossover concept
The ‘crossover concept’ is a theoretical model that explains the balance of CHO and fat usage during sustained exercise
The crossover point is the intensity at which energy from CHO predominates over energy from fats, with further increases in intensity resulting in greater CHO use and decreases fat oxidisation
Low to moderate exercise intensity - trained individuals will delay the switch to CHO at they are better able to utilise fats as a fuel source, resulting in glycogen sparing
Hitting the wall 1- 4
The fuel source used for ATP production is based on the duration and intensity of exercise:
1. Low intensity/rest - stored fats are the main fuel source
2. As intensity of exercise increase, the contribution of muscles glycogen increases to meet the more immediate demands for fuel
3. There is enough glycogen stores in muscles to fuel up to 60 minutes depending on intensity (and also training and and CHO loading). Athletes “hit the wall” when muscle glycogen runs out
4. When muscle glycogen stores run out, the stored liver glycogen becomes the primary fuel source allowing exercise to continue but performance starts to diminish
Hitting the wall 5 -7
- Depletion of liver glycogen affect the brain - decision making ability affected
- Fats now become the primary fuel source and intensity of exercise is reduced as fats require more complex chemical reactions and greater amounts of oxygen
- Depletion of fats results in protein being used as a fuel source
- this is only likely to occur in ultra endurance events
Immediate cardiovascular responses to physical activity 1-6 X4
Increased cardiac output
Increased heart rate
Increased stroke volume
Increased blood pressure
Blood redistribution
Increased arteriovenous oxygen difference
Increased cardiac output / short term (immediate) effects of physical activity (PA)
Immediate cardiovascular responses to physical activity
- Total amount of blood the heart pumps every minute
- Calculated by heart rate x stroke volume
Increased heart rate
Immediate cardiovascular responses to physical activity
- Number of times heart beats per minute
- To provide more rapid supply of fuel and energy to the muscles, heart rate increases during exercise
- This increase is directly proportional to the workload
Increased stroke volume
Immediate cardiovascular responses to physical activity
The amount of blood that is ejected from the left ventricle with each beat of the heart
Increased blood pressure
Immediate cardiovascular responses to physical activity
- Arterioles supplying working muscles vasodilate, so more blood is forced from arterioles into the capillaries surrounding the muscle
- BP sees a significant increase particularly in exercise which use large muscle groups such as running, cycling or swimming
Blood redistribution
Immediate cardiovascular responses to physical activity
- During exercise, arteries open up and contract to allow more or less blood to reach certain areas of the body
- Arteries taking blood to working muscles open up (vasodilate) to allow more blood to the muscles whilst arteries taking blood to non active areas of the body contract (vasoconstrict) to reduce blood flow. This increases the amount of blood available to the working muscles.
- To avoid overheating, the blood acts as a temperature regulator, taking heat from within the body to skin surface, where evaporation of sweat assists in cooling the body.
Increases arteriovenous oxygen difference (a-vO2 diff)
Immediate cardiovascular responses to physical activity
- A comparison of the oxygen in the arteries compared with the veins provides a measurement of muscle oxygen use.
- As more oxygen is extracted by the muscles during exercise, the avO2 difference increases - more oxygen is in the arterioles delivering the blood than is present in venules taking the blood away from the muscle.
- Increased cardiac output to the muscle and extraction of oxygen = greater oxygen availability at the muscle to be used during exercise